function* countAppleSales() {
  var saleList = [3, 7, 5];
  for (var i = 0; i < saleList.length; i++) {
    console.log('>>>11', i)
    yield saleList[i];
    console.log('>>>22', i)
  }
}

var appleStore = countAppleSales(); // Generator { }
console.log(appleStore.next()); // { value: 3, done: false }
console.log(appleStore.next()); // { value: 7, done: false }
console.log(appleStore.next()); // { value: 5, done: false }
console.log(appleStore.next()); // { value: undefined, done: true }


// @testable
// class MyTestableClass {
// }

// function testable(target) {
//   target.isTestable = true;
// }

// MyTestableClass.isTestable // true